1. Field of the Invention
This invention relates to binoculars having a focusing mechanism mounted on the outside of a rearmost bridge connecting the body tubes and particularly to a focusing mechanism including a gear extending to each tube through the bridge and in which focusing is not affected by adjustments made to the distance between the tubes.
2. Description of the Related Technology
DE-PS 154 142 discloses binoculars having two spaced articulably jointed bridges connected to a pair of body tubes housing the optical components of the binoculars. Since the bridges are not connected by a center axle, an open space is formed between the two body tubes and the connecting bridges so that one tube can be enclosed by the user's hand. This reach-through ensures safe handling of the binoculars and in particular considerably facilitates holding and carrying the binoculars with one hand.
In conventional binoculars, the focusing mechanisms are formed by mounting the eyepieces in tubular inserts telescopically displaceable within the binocular's body tubes. These tubular inserts have external toothing, and an internal thread for displacement in the longitudinal direction of the tube. The external toothings are engaged by intermediate gearwheels mounted on the bridge and seated on each of two focusing knobs mounted concentrically and in tandem.
When the body tubes in conventional binoculars are swivelled around the joint axis the focus necessarily changes due to the relative rotation of the gear-wheels and focusing knobs. Conventional binoculars are therefore extremely difficult to handle. In addition, focusing must be effected by simultaneous rotation of the two focusing knobs mounted closely in tandem, which is also difficult.
An alternative binocular focusing scheme uses a hollow double-jointed bridge in which a central focusing device is mounted for operating the focusing mechanism via a gear. The focusing mechanism is mounted in sleeves within the tubes, this configuration known as internal focusing (cf. e.g. DE 39 29 825 C1). Due to the large bridge required to handle this focusing structure, conventional binoculars do not permit a user to reach through between the body tubes. The binoculars are also considered to be unwieldy due to the wide, hollow jointed bridge and the heavy gearing substantially filling said bridge.
Accordingly, there exists a need for a light, easy-to-handle binocular type telescope.